In a mobile communications system, a function that a plurality of terminal devices share one number enables one mobile subscriber international integrated services digital network (ISDN)/public switched telephone network (PSTN) number (MSISDN) to be corresponding to a plurality of subscriber identity module (SIM) cards, where different international mobile subscriber identities (IMSIs) are used for the SIM cards.
In a scenario in which a plurality of SIM cards share one MSISDN, only a maximum of one SIM card is in an active state at a specific time. During IMSI activation of a terminal device that has a SIM card in an idle state, the terminal device may proactively initiate a location update process to activate an IMSI corresponding to the SIM card.
However, in an Internet of Things (IoT) application scenario, for example, a wearable device may be connected to a network by using a direct link such as an long term evolution (LTE) radio access technology. Alternatively, the wearable device may be first connected to a relay node, and then connected to a network by using the relay node. An IMSI used for a SIM card of the wearable device and an IMSI used for a SIM card of the relay node may share a same MSISDN. In this case, if the wearable device proactively initiates a location update process to activate the IMSI corresponding to the SIM card in the wearable device, power consumption of the wearable device is greatly increased. Therefore, an IMSI management method that can be used to reduce power consumption of the wearable device needs to be designed urgently, to meet a requirement of the Internet of Things application scenario.